Semiconductor device in which occurence of slips is suppressed

ABSTRACT

A substrate contains dissolved oxygen at a concentration of not more than 8×10 17  atoms/cm 3  and an impurity which is used as an acceptor or donor at a concentration of not more than 1×10 15  atoms/cm 3 . In the substrate, an oxygen precipitation layer used to suppress occurrence of a slip starting from the rear surface of the substrate is formed. On the substrate, a silicon layer in which circuit elements are formed and which contains dissolved oxygen with at concentration of not more than 8×10 17  atoms/cm 3  and an impurity which is used as an acceptor or donor at a concentration of not more than 1×10 15  atoms/cm 3  is formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is basedupon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2002-273412, filed Sep. 19,2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor device comprising ahigh-resistance substrate with for example, a high-frequency circuitformed thereon.

2. Description of the Related Art

Recently, a system-on-a-chip comprising a semiconductor chip on which aplurality of LSIs are formed has been developed. With the development ofthe system-on-a-chip, not only a digital circuit and a low-frequencyanalog circuit, but also a high-frequency circuit are formed on a singlesubstrate. When a high-frequency circuit is formed on a siliconsubstrate, it is preferable to use a substrate having a high resistance.For example, if an inductor is included in the high-frequency circuit,the Q value of the inductor can be increased. In addition, it ispossible to prevent interference between the inductor and the othercircuits. Also, even if a resistor or capacitor is coupled to thesubstrate, it is possible to prevent a signal from leaking into thesubstrate.

When the concentration of dissolved oxygen in the substrate is high, theoxygen is converted into a donor form and the resistance of thesubstrate is reduced if heat treatment is used when formatting a device.Therefore, a high-resistance substrate is formed and the concentrationof dissolved oxygen in the substrate is reduced. However, if theconcentration of dissolved oxygen is reduced, slips occur in theperipheral portion of the rear surface of the substrate during heattreatment. The slip starts in a portion in contact with a portionsupporting the wafer used as the substrate when the wafer is heattreated in a vertical furnace. If the slip reaches a device formationregion of the front surface of the wafer, a leak occurs and it becomesdifficult to form a satisfactory device.

An example is given in which an SOI device is formed on ahigh-resistance substrate (for example, refer to 2000 SYMPOSIUM ON VLSITECHNOLOGY Digest of Technical Papers pp. 154-155, Jun. 13-15, 2000),although this example is different from an example in which devices areformed in bulk.

Thus, to improve the performance of the high-frequency circuit, it isextremely important to increase the resistance of the substrate.However, if the concentration of dissolved oxygen in the substrate isreduced to form a high-resistance substrate, there is a risk of slipsstarting in portions supporting the substrate during such heat treatmentas an annealing process. Therefore, there is a pressing need to developa semiconductor device in which the occurrence of slips can besuppressed and a device can be formed on the high-resistance substrate.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided asemiconductor device comprising a substrate in which an oxygenprecipitation layer is formed, the substrate containing dissolved oxygenat a concentration of not more than 8×10¹⁷ atoms/cm³ and an impuritywhich acts as an acceptor or donor at a concentration of not more than1×10¹⁵ atoms/cm³, and a silicon layer having circuit elements is formedtherein is formed on the substrate, the silicon layer containingdissolved oxygen at a concentration of not more than 8×10¹⁷ atoms/cm³and an impurity which acts as an acceptor or donor at a concentration ofnot more than 1×10¹⁵ atoms/cm³.

According to another aspect of the invention, there is provided asemiconductor device comprising a substrate containing carbon at aconcentration of not less than 1×10¹⁷ atoms/cm³, dissolved oxygen at aconcentration of not more than 8×10¹⁷ atoms/cm³ and an impurity whichacts as an acceptor or donor at a concentration of not more than 1×10¹⁵atoms/cm³ ₁ and a silicon layer having circuit elements formed thereinis formed on the substrate, the silicon layer containing dissolvedoxygen at a concentration of not more than 8×10¹⁷ atoms/cm³ and animpurity which acts as an acceptor or donor at a concentration of notmore than 1×10¹⁵ atoms/cm³.

According to another aspect of the invention, there is provided asemiconductor device comprising a substrate containing nitrogen at aconcentration of not less than 1×10¹⁴ atoms/cm³, dissolved oxygen at aconcentration of not more than 8×10¹⁷ atoms/cm³ and an impurity whichacts as an acceptor or donor at a concentration of not more than 1×10¹⁵atoms/cm³, and a silicon layer having circuit elements formed therein isformed on the substrate, the silicon layer containing dissolved oxygenat a concentration of not more than 8×10¹⁷ atoms/cm³ and an impuritywhich acts as an acceptor or donor at a concentration of not more than1×10¹⁵ atoms/cm³.

According to another aspect of the invention, there is provided asemiconductor device comprising a substrate containing dissolved oxygenat a concentration of not more than 8×10¹⁷ atoms/cm³ and an impuritywhich acts as an acceptor or donor at a concentration of not more than1×10¹⁵ atoms/cm³, the substrate having a first surface on which circuitelements are formed and a second surface parallel to the first surface,and an impurity layer formed on the second surface of the substrate, theimpurity layer being formed within a range in contact with a supportingportion used to support the substrate during heat treatment.

According to another aspect of the invention, there is provided asemiconductor device comprising a substrate containing dissolved oxygenat a concentration of not more than 8×10¹⁷ atoms/cm³ and an impuritywhich acts as an acceptor or donor at a concentration of not more than1×10¹⁵ atoms/cm³, the substrate having a first surface on which circuitelements are formed and a second surface parallel to the first surface,and an insulating film formed on the second surface of the substrate,the insulating film being formed within a range in contact with asupporting portion used to support the substrate during heat treatment.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross-sectional view showing a semiconductor deviceaccording to a first embodiment of the invention;

FIG. 2 is a cross-sectional view showing a manufacturing step of thesemiconductor device shown in FIG. 1;

FIG. 3 is a cross-sectional view showing a manufacturing step followingthe step shown in FIG. 2;

FIG. 4 is a cross-sectional view showing a semiconductor deviceaccording to a second embodiment of the invention;

FIG. 5 is a cross-sectional view showing a manufacturing step of thesemiconductor device shown in FIG. 4;

FIG. 6 is a cross-sectional view showing a semiconductor deviceaccording to a third embodiment of the invention;

FIG. 7 is a cross-sectional view showing a manufacturing step of thesemiconductor device shown in FIG. 6;

FIG. 8 is a cross-sectional view showing a semiconductor deviceaccording to a fourth embodiment of the invention;

FIG. 9 is a cross-sectional view showing a manufacturing step of thesemiconductor device shown in FIG. 8;

FIG. 10 is a cross-sectional view showing a manufacturing step followingthe step shown in FIG. 9;

FIG. 11 is a cross-sectional view showing a semiconductor deviceaccording to a fifth embodiment of the invention;

FIG. 12 is a cross-sectional view showing a manufacturing step of thesemiconductor device shown in FIG. 11;

FIG. 13 is a cross-sectional view showing a manufacturing step followingthe step shown in FIG. 12;

FIG. 14 is a diagram showing the relationship between the concentrationof dissolved oxygen in the substrate and the resistance of thesubstrate;

FIG. 15 is a circuit diagram showing one example of a high-frequencycircuit to which the invention is applied;

FIG. 16 is a cross-sectional view showing part of a digital/analogmixing integrated circuit to which the invention is applied;

FIG. 17 is a diagram showing the relationship between the resistance ofthe substrate and substrate noise; and

FIG. 18 is a diagram showing the relationship between the resistance ofthe substrate and Q of an inductor.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of this invention will now be described with reference tothe accompanying drawings.

(First Embodiment)

FIG. 1 shows a semiconductor device 10 according to a first embodimentof the invention. The semi-conductor device 10 includes a siliconsubstrate 11 having an oxygen precipitation layer 12 formed therein. Forexample, the substrate 11 is a high-resistance substrate having aresistance of 1000Ω or more.

A silicon layer 13 is formed on the surface of the substrate 11. Thesilicon layer 13 has a dissolved oxygen concentration of 8×10¹⁷atoms/cm³ or less and an impurity concentration of 1×10¹⁵ atoms/cm³ orless. Since the dissolved oxygen concentration is less than or equal to8×10¹⁷ atoms/cm³, the silicon layer 13 has a high resistance of 1000Ω ormore, like the substrate 11. The film thickness of-the silicon layer 13is 1 μm to 10 μm, for example. The film thickness of the silicon layer13 may be selectively set according to the depth of the device to beformed and the distance from the oxygen precipitation layer 12 to thebottom of the device, and is preferably set to 4 μm or less. An analogcircuit, digital circuit and high-frequency circuit are formed in thesilicon layer 13, for example.

FIGS. 2 and 3 show a manufacturing method of the semiconductor device10.

FIG. 2 shows the semiconductor device 10 prior to the heat treatment.The concentration of dissolved oxygen in the substrate 11 is 1×10¹⁸atoms/cm³ or more and the impurity concentration thereof is 1×10¹⁵atoms/cm³ or less, for example. By annealing the substrate 11, oxygen isprecipitated. In the annealing process for the precipitation of oxygen,the temperature is set at 1000° C. or more; and the processing time, 10hours or more. That is, the conditions are so set that the concentrationof dissolved oxygen in the substrate 11 after the annealing process willbe less than or equal to 8×10¹⁷ atoms/cm³.

FIG. 3 shows a state in which the oxygen precipitation layer 12 appearsin the substrate 11. After this, as shown in FIG. 1, a silicon layer 13is formed on the substrate 11 by means of an epitaxial growth method,for example. The silicon layer 13 thus formed has the above dissolvedoxygen and impurity concentrations. The dissolved oxygen concentrationis determined according to the dissolved oxygen concentration of thesubstrate and the impurity concentration is controlled according to theconcentration of mixed gas when the epitaxial growth method isperformed, for example. Then, a device containing for example, ahigh-frequency circuit, is formed using the above substrate.

Dissolved oxygen refers to oxygen in which oxygen atoms are scattered ina silicon crystal; precipitation oxygen refers to a chemical compoundformed by oxygen atoms reacting with silicon. Therefore, precipitationoxygen is stable and is not converted into a donor form by heattreatment. The precipitation oxygen in the substrate can be easilydetected using a scanning electron microscope.

According to the first embodiment, the precipitation oxygen layer 12 isformed in the substrate having high resistance. The precipitation oxygenlayer 12 suppresses extension of a slip when the substrate is subjectedto heat treatment. Therefore, a slip on the rear surface of thesubstrate 11 can be prevented from reaching the front surface.

The precipitation oxygen layer 12 is formed in the substrate 11 bymaking the concentration of dissolved oxygen in the substrate higherthan normal and so causing the dissolved oxygen to precipitate. Inaddition, the precipitation oxygen is not converted into donor form.Therefore, the substrate 11 can have the desired high resistance afterthe precipitation oxygen layer 12 has been formed.

Further, a semiconductor device with excellent high-frequencycharacteristics can be formed by forming on the substrate 11 a siliconlayer 13 having high resistance, like the substrate 11, and forming adevice using the substrate having the silicon layer 13.

(Second Embodiment)

FIGS. 4 and 5 show a second embodiment of the invention.

In the semiconductor device 10 shown in FIG. 4, for example, a siliconsubstrate 11 contains an impurity 20 such as carbon which does not actas an acceptor or donor for the silicon. The concentration of carbon is1×10¹⁶ atoms/cm³ or more, for example, and preferably 5×10¹⁷ atoms/cm³or more. Further, the concentration of dissolved oxygen in the substrate11 is 8×10¹⁷ atoms/cm³ or less, for example, and the concentration of animpurity which acts as an acceptor or donor is 1×10¹⁵ atoms/cm³ or less,for example. Since the concentration of dissolved oxygen in thesubstrate 11 is less than or equal to 8×10¹⁷ atoms/cm³, the substrate 11has a high resistance of 1000Ω, for example.

A silicon layer 21 is formed on the substrate 11. For example, thesilicon layer 21 contains carbon at a concentration of 1×10¹⁷ atoms/cm³or less, dissolved oxygen at a concentration of 8×10¹⁷ atoms/cm³ orless, and an impurity which acts as an acceptor or donor. The impurityconcentration is 1×10¹⁵ atoms/cm³ or less, for example. Since thedissolved oxygen concentration is less than or equal to 8×10¹⁷atoms/cm³, the silicon layer 21 also has a high resistance of 1000Ω ormore. The film thickness of the silicon layer 21 is 1 μm to 10 μm, forexample, and is preferably 4 μm or less. An analog circuit, digitalcircuit and high-frequency circuit, for example, are formed in thesilicon layer 21.

FIG. 5 shows a manufacturing method of the semiconductor device of FIG.4.

First, for example, carbon used as the impurity 20 and an impurityacting as an acceptor or donor are doped into the substrate 11. Variousimpurity doping methods are possible. For example, the impurity can bedoped into a wafer when the wafer is formed, or it can be doped into thewafer by means of an ion implantation technique, for example, after thewafer has been formed.

After this, as shown in FIG. 4, a silicon layer 21 is formed on thesubstrate 11 by means of an epitaxial growth method, for example. Thesilicon layer 21 thus formed has the above dissolved oxygen and impurityconcentrations. The dissolved oxygen concentration is determinedaccording to the dissolved oxygen concentration of the substrates, andthe impurity and carbon concentrations are controlled according to theconcentration of mixed gas when the epitaxial growth method isperformed, for example. In this case, it is preferable that theconcentration of carbon in the silicon layer 21 becomes lower.

According to the second embodiment, the substrate 11 having a highresistance of 1000Ω, for example, contains carbon at a concentration of5×10¹⁶ atoms/cm³ or more. When the silicon substrate 11 contains carbon,a slip in the substrate becomes shorter as the carbon concentrationincreases. For example, when the carbon concentration in the substrateis 5×10¹⁶ atoms/cm³, the length of a slip in the substrate isapproximately 60 μm; but when the carbon concentration in the substrateis 1×10¹⁷ atoms/cm³, the length of the slip is approximately 20 μm. Ifthe carbon concentration in the substrate is further increased, the slipbecomes shorter. Therefore, occurrence of a slip can be suppressed byincluding carbon at a concentration of 5×10¹⁶ atoms/cm³ or more in thesubstrate 11 of high resistance.

In addition, a semiconductor device which has excellent high-frequencycharacteristics can be formed by forming on the substrate 11 a siliconlayer 21 having a high resistance, like the substrate 11, and forming adevice using the substrate 11 having the silicon layer 21.

(Third Embodiment)

FIGS. 6 and 7 show a third embodiment of the invention. While, in thesecond embodiment, the substrate 11 contains carbon, in the thirdembodiment, the substrate 11 contains nitrogen.

In the semiconductor device 10 shown in FIG. 6, for example, the siliconsubstrate 11 contains an impurity 22 such as nitrogen which does notacts as an acceptor or donor for silicon. The concentration of nitrogenis 5×10¹³ atoms/cm³ or more. Further, the dissolved oxygen concentrationin the substrate 11 is 8×10¹⁷ atoms/cm³ or less, for example, and theconcentration of an impurity which is used as an acceptor or donor is1×10¹⁵ atoms/cm³ or less, for example. Since the concentration ofdissolved oxygen in the substrate 11 is less than or equal to 8×10¹⁷atoms/cm³, the substrate 11 has a high resistance of 1000Ω or more, forexample.

A silicon layer 23 is formed on the substrate 11. For example, thesilicon layer 23 contains nitrogen having a concentration of 5×10¹³atoms/cm³ or less, dissolved oxygen at a concentration of 8×10¹⁷atoms/cm³ or less, and an impurity which is used as an acceptor ordonor. The impurity concentration is 1×10¹⁵ atoms/cm³ or less, forexample. Since the dissolved oxygen concentration is less than or equalto 8×10¹⁷ atoms/cm³, the silicon layer 23 also has a high resistance of1000Ω or more. The film thickness of the silicon layer 23 is 1 μm to 10μm, for example, and is preferably 4 μm or less. An analog circuit,digital circuit and high-frequency circuit are formed on the substrate11 having the silicon layer 23, for example.

FIG. 7 shows a-manufacturing method of the semiconductor device of FIG.6.

First, for example, nitrogen used as the impurity 22 and an impurityused as an acceptor or donor are doped into the substrate 11. Variousimpurity doping methods are possible. For example, impurity can be dopedinto a wafer when the wafer is formed, or impurity can be doped into awafer by means of an ion implantation technique, for example, after thewafer has been formed.

After this, as shown in FIG. 6, a silicon layer 23 is formed on thesubstrate 11 by means of an epitaxial growth method, for example. Thethus formed silicon layer 23 has the above dissolved oxygen and impurityconcentrations. The dissolved oxygen concentration is determinedaccording to the dissolved oxygen concentration of the substrate and theimpurity concentration and nitrogen concentration are controlledaccording to the concentration of mixed gas when the epitaxial growthmethod is performed, for example. In this case, it is more preferable asthe concentration of nitrogen in the silicon layer 21 becomes lower. Ananalog circuit, digital circuit and high-frequency circuit are formed onthe substrate 11 having the silicon layer 23, for example.

According to the third embodiment, the same effect as that obtained inthe second embodiment can be attained. That is, when the siliconsubstrate 11 containing nitrogen is used, a slip in the substratebecomes shorter as the nitrogen concentration increases. For example,when the nitrogen concentration in the substrate is 5×10¹³ atoms/cm³,the length of a slip in the substrate is approximately 60 μm; but whenthe nitrogen concentration in the substrate is 1×10¹⁵ atoms/cm³, thelength of the slip is approximately 55 μm. If the nitrogen concentrationin the substrate is further increased, the slip becomes shorter.Therefore, occurrence of a slip can be suppressed by including nitrogenat a concentration of 5×10¹³ atoms/cm³ or more in the substrate 11 ofhigh resistance.

(Fourth Embodiment)

FIGS. 8, 9 and 10 show a fourth embodiment of the invention.

In FIG. 8, a silicon substrate 31 contains dissolved oxygen at aconcentration of 8×10¹⁷ atoms/cm³ or less and impurity which is used asan acceptor or donor at a concentration of 1×10¹⁵ atoms/cm³ or less.Since the dissolved oxygen concentration is less than or equal to 8×10¹⁷atoms/cm³, the substrate 31 has a high resistance of 1000Ω or more, forexample. Circuit elements (not shown) are formed on the front surface(first surface) 31 a of the substrate 31. An impurity layer 32 is formedon the outer peripheral portion of the rear surface (second surface) 31b which is parallel to the front surface 31 a. The position at which theimpurity layer 32 is formed is determined according to the portion ofthe substrate 31 with which a supporting portion is set in contact atduring the heat treatment carried out when manufacturing the device, forexample. Generally, the supporting portion contacts the rear surface ofthe substrate 31. Therefore, the impurity layer 32 is formed by dopingan impurity such as carbon or nitrogen which is not used as an acceptoror donor with respect to silicon. The width L1 and depth L2 of theimpurity layer 32 are determined according to the range of the substrate31 in which the supporting portion contacts the substrate. Therefore,the width L1 must be larger than the range in which the supportingportion contacts the substrate. More specifically, the width L1 is setto 3 mm to 8 mm, and is generally set to approximately 5 mm, and thedepth L2 is set to 1 μm to 2 μm, for example.

As impurity to be doped, carbon or nitrogen is used, for example. Theconcentration is 5×10¹⁶ atoms/cm³ or more if carbon is used, and theconcentration is 5×10¹³ atoms/cm³ or more if nitrogen is used.

FIGS. 9 and 10 show a fabrication method of the substrate.

In FIG. 9, the silicon substrate 31 contains dissolved oxygen at aconcentration of 8×10¹⁷ atoms/cm³ or less and an impurity which is usedas an acceptor or donor at a concentration of 1×10¹⁵ atoms/cm³ or less.A mask is formed on the rear surface 31 b of the substrate 31.

FIG. 10 shows a mask 33 formed on the rear surface 31 b of the substrate31. The mask 33 exposes a region of the width L1 from the outer edgeportion of the substrate 31. Carbon or nitrogen is ion-implanted intothe rear surface portion 31 b of the substrate 31 by use means the mask33. The ion-implantation process is performed at a concentration of5×10¹⁶ atoms/cm³ or more if carbon is used, and at a concentration of5×10¹³ atoms/cm³ or more if nitrogen is used. After this, the mask 33 isremoved and the substrate shown in FIG. 8 is completed. An analogcircuit, digital circuit and high-frequency circuit are formed on thefront surface of the substrate 31 having the high resistance, forexample.

According to the fourth embodiment, the impurity layer 32 is formed onthe rear surface of the substrate 31 having high resistance in aposition corresponding to the portion of the substrate in contact withthe supporting portion during annealing. Therefore, a slip in thesubstrate 31 during annealing can be prevented. Thus, since a slip whichreaches the front surface region of the substrate 31 is not formed, asemiconductor device whit excellent high-frequency characteristics canbe formed by forming a device using the substrate 31.

(Fifth Embodiment)

FIGS. 11, 12 and 13 show a fifth embodiment of the invention.

In FIG. 11, since the concentration of dissolved oxygen in a siliconsubstrate 31 is less than or equal to 8×10¹⁷ atoms/cm³, the substrate 31has a high resistance of 1000Ω or more. Circuit elements not shown areformed on the front surface (first surface) 31 a of the substrate 31. Anoxide film 43 is formed on the outer peripheral portion of the rearsurface (second surface) 31 b which is parallel to the front surface 31a. The position at which the oxide film 43 is formed is determinedaccording to the portion of the substrate 31 in contact with thesupporting portion during the heat treatment performed whenmanufacturing the device, for example. Therefore, the oxide film 43 isformed in a range larger than the area in contact with the supportingportion. For example, a nitride film 42 is formed on a portion of thesubstrate 31 on which the oxide film 43 is not formed. Further, an oxidefilm 44 is formed in connection with the oxide film 43 on the peripheralsurface of the substrate 31. The width L1 and depth L2 of the oxide film43 are the same as those in the case of the fourth embodiment.

FIGS. 12 and 13 show a fabrication method of the substrate.

In FIG. 12, the silicon substrate 31 contains dissolved oxygen at aconcentration of 8×10¹⁷ atoms/cm³ or less and an impurity which is usedas an acceptor or donor at a concentration of 1×10¹⁵ atoms/cm³ or less.An oxide film 41 is formed on the front surface, rear surface andperipheral surfaces of the substrate 31. The oxide film 41 is formed bysubjecting the substrate 31 to thermal oxidation, for example. A filmused as an anti-oxidation film, such as a silicon nitride film 42, isformed on the entire surface of the oxide film 41.

Next, as shown in FIG. 13, portions of the oxide film 41 and siliconnitride film 42 which lie on the peripheral surface of the substrate 31and in the range with which the supporting portion contacts are removedby patterning the oxide film 41 and silicon nitride film 42. That is,the peripheral surface of the substrate 31 and the outer peripheralportion of the rear surface are exposed.

After this, the substrate 31 is subjected to thermal oxidation by theLOCOS method to form oxide films 43, 44. Then, as shown in FIG. 11,portions of the oxide film 41 and silicon nitride film 42 which lie onthe front surface of the substrate 31 are removed. Next, for example, ananalog circuit, digital circuit and high-frequency circuit are formed onthe front surface of the substrate 31 having high resistance.

According to the fifth embodiment, the oxide film 43 is formed on therear surface of the substrate 31 having high resistance in a positioncorresponding to the portion of the substrate in contact with thesupporting portion during annealing. Therefore, a slip in the substrate31 during annealing can be prevented. Thus, since a slip which reachesthe front surface region of the substrate 31 is not formed in thesubstrate 31, a semiconductor device with excellent high-frequencycharacteristics can be formed by forming a device by use of thesubstrate 31.

FIG. 14 shows the relationship between the concentration of dissolvedoxygen in the substrate and the resistance of the substrate. As shown inFIG. 14, the resistance decreases as the concentration of dissolvedoxygen in the substrate increase. However, the rate of occurrence of aslip is reduced. Conversely, the resistance increases as theconcentration of dissolved oxygen in the substrate decreases. However,the rate of occurrence of a slip is increased.

In the first to fifth embodiments, the concentration of dissolved oxygenin the substrate is reduced to increase the resistance of the substrate.In the first embodiment, to suppress a slip in the substrate, the oxygenprecipitation layer is formed and, in the second and third embodiments,an impurity which is not used as the acceptor or donor is doped into thesubstrate. Further, in the fourth and fifth embodiments, the impuritylayer or oxide film is formed on the rear surface of the substrate andthe outer peripheral portion thereof to prevent a slip.

In the first to fifth embodiments, the concentration of dissolved oxygenin the substrate is made less than or equal to 8×10¹⁷ atoms/cm³.Therefore, the resistance of the substrate is set to 1000Ω or more. Whena high-frequency circuit is formed, it is more preferable that theresistance of the substrate be made higher. However, depending on theapplication thereof, it is possible to use a substrate having aresistance of approximately 500Ω. As can be clearly seen from FIG. 14,it is possible to attain a resistance of 500Ω by making theconcentration of dissolved oxygen in the substrate 8×10¹⁷ atoms/cm³ orless.

FIG. 15 shows a voltage controlled oscillator as one example of ahigh-frequency circuit formed on the substrate 11, 31 having highresistance. The voltage-controlled oscillator includes a spiral-forminductor 51, variable-capacitance diode 52, a plurality of N-channelMOSFETs 53, a plurality of P-channel MOSFETs 54 and a resistor 55.

FIG. 16 schematically shows part of a digital/analog mixing integratedcircuit using the voltage-controlled oscillator shown in FIG. 15.Circuit elements configuring the integrated circuit are formed on thesubstrate 11, 31 or in the silicon layer 13, 21, 23. That is, thecircuit elements are formed in the bulk of the high-resistancesubstrate. Thus, by forming the circuit elements in the high-resistancesubstrate, substrate noise can be reduced and noise from the digitalcircuit can be kept out of the analog circuit.

FIG. 17 shows the relationship between the resistance of the substrateand substrate noise. The characteristic diagram is obtained by plottingagainst frequency the intensity of the signal between the well in whichthe digital circuit is formed and the well in which the analog circuitis formed. As can be clearly seen from FIG. 17, when the resistivity ofthe substrate is 1000 Ω-cm, the noise reduction effect with respect tothe high-frequency signal is large in comparison with the case whereinthe resistivity is 5 Ω-cm.

Further, as shown in FIG. 16, the inductor 51 is formed in a region inwhich the well of the substrate 11, 31 is not formed. The resistance ofthe well is lower than the resistance of the substrate. Therefore, the Qvalue of the inductor can be increased by forming the inductor 51 in theregion in which the well of the substrate 11, 31 is not formed and whichhas high resistance.

FIG. 18 shows the relationship between the resistance of the substrateand Q of the inductor. It can be clearly seen from FIG. 18 that aninductor formed in the substrate of resistivity 1000 Ω-cm has a larger Qvalue than an inductor formed in the substrate of resistivity 1 Ω-cm.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A semiconductor device comprising: a substrate having an oxygenprecipitation layer formed therein, the substrate containing dissolvedoxygen at a concentration of not more than 8×10¹⁷ atoms/cm³ and animpurity which is used as an acceptor or donor at a concentration of notmore than 1×10¹⁵ atoms/cm³, and a silicon layer formed on the substrateand having circuit elements formed therein, the silicon layer containingdissolved oxygen at a concentration of not more than 8×10¹⁷ atoms/cm³and an impurity which is used as an acceptor or donor at a concentrationof not more than 1×10¹⁵ atoms/cm³.
 2. A device according to claim 1,wherein the film thickness of the silicon layer is 1 μm to 10 μm.
 3. Adevice according to claim 1, wherein the film thickness of the siliconlayer is not more than 4 μm.
 4. A device according to claim 1, whereinthe silicon layer is an epitaxial layer.
 5. A device according to claim1, wherein the circuit elements include an inductor formed in a regionwhich is formed above the substrate and in which no well is formed.6-22. (canceled)